1. Field of the Invention
The present invention relates to a manufacturing method of a liquid crystal panel and a surface treatment method of an alignment film, and more particularly, relates to a surface treatment method for suppressing alignment defects which cause image irregularities of liquid crystal display devices.
2. Description of the Related Art
An electronic device called liquid crystal on silicon (LCOS) which is represented by an active matrix liquid crystal display panel is generally manufactured by sequentially performing many treatment processes on a substrate, such as oxide, silicon, sapphire, or glass. The treatment processes, for example, may include cleaning, thin-film formation, etching, ion implantation, thermal processing, porous film formation, alignment film formation, application of liquid crystal sealing agent, and liquid crystal injection.
In general, all the treatment processes are performed in respective manufacturing apparatuses which are disposed in a clean room. In the treatment processes, when semiconductor substrates are transported from one process to another process, the substrates are exposed to the atmosphere in the clean room. A manufacturing method of an active matrix liquid crystal display panel has been disclosed.
In addition, in order to remove moisture in a semiconductor device manufacturing process, a method has been disclosed in Japanese Patent Laid-Open Nos. 2004-310037 and 2005-62877 in which a substrate is irradiated with a noble gas or a hydrogen active species.
However, in a liquid crystal panel manufactured in accordance with a method of the related art, image irregularities were generated in some cases. In particular, as a liquid crystal projector application, when the liquid crystal panel was continuously irradiated with intensive light, apparent image irregularities sometimes occurred after the panel was used for a long period of time.
According to intensive research and consideration carried out by the inventors of the present invention, it is believed that moisture which adheres to an alignment film aligning liquid crystal molecules is one of the reasons causing image irregularities of a liquid crystal panel.
For example, when a solid substance is exposed to the atmosphere of a clean room, it adsorbs moisture in the clean room on the surface thereof quickly. In a liquid crystal panel, oxide, such as a silicon oxide, which is formed by oblique deposition, is sometimes used as an inorganic alignment film. In this case, the inorganic alignment film quickly adsorbs moisture in the atmosphere when it is recovered from a deposition vacuum chamber. In particular, since the oblique deposition film is a film which is grown in an oblique direction with respect to a substrate, the influence of moisture adsorption as described above is considerable. As a result, the adsorbed moisture desorbs as steam in a subsequent step and then diffuses into the liquid crystal, resulting in image irregularities and degradation in light durability and the like.
As described above, it was found that moisture molecules, which adsorb on the inorganic alignment film, variously affect the properties of a liquid crystal device and are partly responsible for causing image irregularities. In addition, it was also found that, after the process for forming this alignment film is finished, the adsorption of moisture must be suppressed.